Starry Sky Stacker

Starry Sky Stacker, from the developers of Starry Landscape Stacker, is a Mac-only image stacking program that allows you to stack, or combine, images of deep-sky objects taken with a star tracker to reduce noise and enhance detail. You can also stack these deep sky images in Starry Landscape stacker, Deep Sky Stacker, Pixinsight and even Photoshop to name a few. Starry Sky Stacker is an efficient and user-friendly program that currently costs $25 in the app store. This article is not a paid review; I bought the program with my hard-earned money.

As an Amazon Associate, earns from qualifying purchases.

The Andromeda Galaxy loaded into Starry Sky Stacker.
Images of the Andromeda Galaxy imported into Starry Sky Stacker before running the stacking algorithm.

What Does Starry Sky Stacker Do?

Deep-sky imaging consists of taking a series of images, sometimes a few hundred, over many hours and combining them to create one stunning final image. Starry Sky Stacker reads your set of images, aligns them, estimates the quality and sorts them by the image quality. By default, the program uses the best half of your pictures but provides you a slider so that you can choose to add or subtract from the total number of images used. If you adjust the slider, it will keep that adjustment for future photos. The preview image will always be the one with the lowest quality ranking. This feature alone makes the software worth the price. Instead of culling through hundreds of photos Starry Sky Stacker does that for you! If you attempt to use Starry Landscape Stacker or Photoshop to stack these images, you will have to cull through your images beforehand.

Let’s Get Started

To get started, I’ve exported all of my images as 16-bit, uncompressed, TIFF files from Lightroom since Starry Landscape Stacker does not support RAW files.

The export dialog box from Lightroom.

Once you open Starry Sky Stacker, you’ll be prompted to select your images. Be sure to check the “Display the image classification table after opening” dialog box. Doing this allows you to review the frames just in case some of them were not classified correctly. In my experience, the software usually does a good job, but sometimes it’ll throw you a curveball! It’s worth your time to double-check the classification.

Starry Sky Stacker Import Dialog.
Left: The import dialog box showing the classification checkbox.
Right: This box lets you adjust the image classification in case the program made a mistake.

The Lights, the Darks, and Flats

Starry Sky Stacker supports Light, Dark and Flat frames. Light frames are regular night sky exposures. Dark frames are used to subtract hot pixels and other thermal noise from your images.  Flat frames remove vignetting. Bias frames are not supported.

What is a Flat Frame?

If you’ve ever taken a photo of a bright blue sky, you might have noticed that the lens naturally vignettes in the corners. Flat frames will remove this vignetting. If you leave your rig set up until morning, you can use a clear blue sky to take your flat frames. Flat frames are shot at the same ISO, aperture, focal length and focus as your light frames. Shutter speed does not matter. You’ll want a bright light that evenly illuminates your frame.

Instead of waiting for the morning, I like to pull up an all-white screen on my iPad and turn the brightness to 100%. I then put this directly over the front of my lens. Put your camera in aperture priority mode; this will let the camera choose your shutter speed. Keeping the same setting mentioned above, take a series of 20 flat frames. You can shot more or less if you wish, but I usually stick with 20.

What is a Dark Frame?

Once you start doing deep-sky imaging, you’ll quickly learn the importance of dark frames. As I mentioned above, dark frames are used to subtract hot pixels and thermal noise from your images. The difference between your light frames and your dark frames is the lens cap. After you’re done taking your regular light frames, don’t touch anything, put the lens cap on and take a series of dark frames. Blocking the light from the sensor will create a black, or “dark,” frame. Any data in this image that is not black does not belong and is subtracted from your light frame. Again, I usually take 20 dark frames, but you can shoot more or less if you wish. Starry Sky Stacker will process these individually without any issues.

Mastering the Flats

Before importing flat frames, you’ll have to create a master flat frame. To do so, import all of your flat frames and Starry Sky Stacker will recognize them, and automatically prompt you to save a master flat file.

Flat frames prompt.
After importing my 20 flat frames, Starry Sky Stacker automatically prompted me to save a master flat file.

How Starry Sky Stacker Works

Once you’ve created your master flat file, it’s time to import all of your images. I have 105 light frames of the Pleiades, 20 dark frames and a master flat frame created from 20 flat frames images. I made a separate folder on my desktop for all my photos making the import process a piece of cake. Double-check the classification of your frames.

The importing, aligning and sorting process can take some time. So, this will depend on how many images you have and how powerful your machine is. With my modest 2017 MacBook Pro, this process didn’t take long at all. Attempting to open the same 145 TIFF files in photoshop would have been a nightmare.

Starry Sky Stacker Quality Slider
The quality slider. This will show you how many images will be used to create the final composite image.

From here, it’s as simple as adjusting the quality slider until you’re happy with the results. Keep in mind, at this point; you do not see the stacked image. Instead, you see the photo with the lowest quality ranking from your selected images. If the image displayed has star trails, you can choose to exclude it by clicking the exclude button or by sliding the quality slider to the left.

Happy with what you see? Hit composite! It’s that easy. Starry Sky Stacker will composite the images and give you the option of which stacking algorithm you want to use. The choices are simple; Mean, Median, Dark Median, Max, and Min. I usually stick with Mean or Median, but feel free to try them for yourself.

A Starry Landscape Stacker Replacement?

Starry Landscape Stacker does a pretty good job by itself. If you only plan to stack a dozen or so deep-sky images, then I don’t see a need for the upgrade. Starry Landscape Stacker also supports Light, Dark, Flat and Bias frames, so it can handle more than you think. If you’re planning to stack a large number of images, however, I would go ahead and invest in Starry Sky Stacker. For a free trial of Starry Landscape Stacker, click here.

Why Not Just Use Photoshop?

Photoshop is a very potent tool, and no matter what stacking software I use, my images always end up in Photoshop. The biggest issue I have with Photoshop is its speed when it comes to processing large amounts of TIFF files. Auto aligning 100 images, converting them to a smart object and applying a mean or median filter in Photoshop will leave you quite a bit of time to knock out some household chores. Want to try out a free trial of Photoshop? Click here.

Maybe PixInsight

I’ve not used PixInsight, but I’ve watched several hours of tutorial videos on youtube for comparison. There is no doubt of the capability of PixInsight, but there does seem to be a steep learning curve. To learn more about PixInsight, click here.

But I Have a PC – then try Deep Sky Stacker!

Deep Sky Stacker is a Windows-only program so I was unable to test this one. Although, this would probably be my program of choice if I had a Windows PC. Deep Sky Stacker has a reputation that speaks for itself, and it’s free! To check out and download Deep Sky Stacker, click here.

Completed photo - The Pleiades - Made from 105 light frames with 20 dark frames and a flat-field frame by Starry Sky Stacker 1.2.0. Algorithm: Median
The Pleiades – Made from 105 light frames with 20 dark frames and a flat-field frame by Starry Sky Stacker 1.2.0. Algorithm: Median

My Conclusions

Starry Sky Stacker is a simple, straight to the point program and I like that. No bells or whistles here. It delivers what it promises in a frustration-free, quick to use, and affordable program. If you’re a Mac user and plan on stacking large numbers of tracked night sky images, then I would highly recommend Starry Sky Stacker! Click here to try a free trial of Starry Sky Stacker for yourself!

If you’ve tried Starry Sky Stacker, let me know in the comments below. If not, would you? Why or why not?

Dean Vinson


  1. Thanks! I love how you kept everything simple. I always wonder what a flat frame was. Now I know. 🙂
    I have Deep Sky Stacker, but I honestly don’t know enough about it to really compare it. Perhaps someday!

    • For stuff like this, Flat Frames work a lot better than the profile correction in Lightroom or photoshop. I find that my photos get a weird “grid” style pattern if I stretch the data a lot after using profile corrections. That doesn’t happen with Flat Frames. I have an ancient PC, I might see if it’s capable or running Deep Sky Stacker. Assuming it still works! I haven’t turned it on in YEARS.

Comments are closed.